Windscreen

ABSTRACT

A glazing element ( 12 ) for an opening defined by opaque boundaries ( 13 ) has an edge region (E) shaped to divert light passing through it in a sense such as to enlarge the field of view through the opening. For this purpose the bounding surfaces ( 33, 34 ) of the element ( 12 ) diverge towards the edge thereof in the edge region (E). The same effect can be achieved by an element ( 25 ) adhered to or otherwise held in position to the surface of the element ( 12 ) in the edge region (E).

The present invention relates generally to improvements in opticalsystems, and in particular to optical systems involving openings definedby opaque boundaries and glazed with one or more glazing elements.

The opaque boundaries of glazed openings or apertures constitute atermination or interruption in the field of view available through theopening. This is widely recognised and accommodated in mostcircumstances by the ability of the observer to change position therebyvarying the field of view through the opening. There are, however,circumstances where the observer's ability to change his field of viewis limited and/or the field-limiting effect of the opaque boundary is ofmore than usually critical importance.

Window apertures often contain frames or glazing bars which act as lightbarriers to interrupt the field of view available through the aperture.Usually this is of little or no consequence, and the restricted field ofview is acceptable; at other times it is possible, as mentioned above,to overcome the obscuration by adjusting the observation position.Furthermore, in unassisted binocular vision, if the barrier is narrowerthan the inter-ocular distance (about 60 mm) one or other eye cangenerally receive light from objects which the other eye cannot seebecause of the obscuration due to the barrier. In some viewing tasks,however, the ability to observe areas obscured by glazing bars oraperture boundaries does become critical. If the barrier is wider thanthe interocular distance and it is not desirable or possible for theobserver to adjust the observation position in order to mitigate theobscuration created by the barrier the problem is exacerbated.

The present invention seeks to provide means by which the field of viewthrough an opening obscured by opaque boundaries can be enlarged evenfor a viewer having a fixed observation position.

This is achieved, according to the invention, by providing a glazingelement for an opening defined by opaque boundaries, having orincorporating means for diverting light passing through an edge regionof the opening whereby to enlarge the field of view through the opening.The said means for diverting light may be a separate element which canbe positioned appropriately in relation to the edge region, or may be aspecific conformation of the edge region itself. In an opening definedby rectilinear boundaries, the term “edge region” will be understood torefer to an edge defined by one rectilinear boundary, and not theentirety of the boundary of the opening. In other words, in the case ofa rectangular or square opening, the “edge region” may be a region alongone (or more) side (or sides) of the opening whilst other sides of theopening have no such view-enlarging arrangement.

The present invention finds particular application in the automotiveindustry where motor vehicle windows are bounded by frame parts of thevehicle which, for reasons of strength and rigidity, have to have acertain minimum thickness. This applies particularly to the so-called Aand B pillars, namely the pillars on either side of the windscreen (theA pillars) and the pillars between the front and rear doors (the Bpillars). It is the A pillars which are of particular concern since theydefine the lateral extent of the driver's field of view forwardlythrough the windscreen, which is the most critical from a safety pointof view. In addition, the A pillars are not vertical, but usually rakedat an angle which, in modern vehicles, approaches 45 degrees in order toaccommodate the inclination of the windscreen for aerodynamic purposes.This means that the lateral extent of the obscuration caused by the Apillar is in fact greater than its transverse thickness, and furtherincreased by the fact that the upper part of the A pillar is closer tothe observer than the lower part, and therefore subtends a greaterhorizontal, angle at the observer's eye for a given width.

Although the driver of a motor vehicle has a certain freedom to move hishead in order to minimise the effect of the barrier constituted by the Apillars, such movement requires a certain amount of time, and alsorelies on the driver being aware of the presence or possible presence ofan object in that part of his field of view obscured by the A pillars.If the driver is unaware of the presence of an object in the obscuredpart of his field of view the fact that it would have been possible toobserve it by movement of the head is irrelevant. Moreover, situationscan arise, when two objects are in relative motion, in which theobscuration region moves in synchronism with the obscured object so thatthe latter remains out of the field of view of the driver for anextended period thereby increasing a potentially hazardous situation.

The principles of the present invention have particular application tothe windscreen of a motor vehicle obscured at its lateral peripheralregions by thick A pillars since the presence of light-diverting meansin or associated with each lateral edge region of the vehicle can makeit possible for an observer effectively to have a field of view in whichthe obscuration effect of the A pillars is at least minimised and, insome cases, cancelled altogether.

By providing a glazing element as defined hereinabove, having means fordiverting light passing through an edge region thereof, the observer mayview otherwise obscured objects without the need for movement of thehead.

In a preferred embodiment of the invention the means for diverting lightpassing through an edge region of the glazing element is integrallyformed with the said element. However, the means for diverting lightpassing through an edge region of the element may be formed separatelyfrom the said element, and fixed, attached or otherwise held in positionor relative juxtaposition with respect thereto.

In essence, the present invention provides a glazing element adapted tofit into an opening defined by opaque boundaries and having a centralregion through which light can pass substantially undeviated and atleast one edge region which diverts light through an angle such as tobring its apparent direction, that is the direction of the refractedlight, when projected back in a straight line through the refractor,closer to the central region of the opening, thus in effect, causing thelight at the edges of the opening to bend around the glazing element asit passes through the refractor from an object towards the observer. Thediversion of light is in practice achieved by refraction, and the anglethrough which the light is diverted may be greater closer to the edge ofthe element. In fact, the angle through which the light is divertedpreferably decreases away from the edge of the element smoothly to apoint where zero diversion takes place. In other words, thelight-diverting means preferably introduces no step-change in lightdiversion at its edge remote from the boundary. This may be achieved,for example, by making the light-diverting effect vary over the width ofthe light diverting means. In the case of a refractor this can beachieved by varying the inclination of the surfaces of the refractorsuch that it is zero (that is the surfaces are substantially parallel)at a point inward from the boundary, and increases progressively towardsthe boundary. This creates what may be considered as a negative lens,and in the case of a motor vehicle windscreen, the negative lens may besubstantially cylindrical. Because the boundary of the windscreen isinclined to the vertical, however, it is preferred that the axis of thecylindrical lens is not parallel to the boundary itself, but inclined atan angle such as to result in the major plane of magnification (negativemagnification, of course, it being a negative lens) of the image by thecylindrical lens being closer to the horizontal, preferably beinghorizontal.

In a preferred embodiment of the invention the glazing element comprisesat least two layers of optically transparent material joinedface-to-face over substantially the whole area thereof, the edge regionof each of the said two layers being formed such that the two layersdiverge from one another towards the periphery of the said element withan optical medium of appropriate refractive index between them wherebyto form a negative cylindrical lens over the said edge region. This hasthe advantage that there is no surface discontinuity between the regionof the glazing element over which no light diversion takes place and theregion of the element at which light is diverted.

The diverging peripheral regions of the glazing element layers may beheld apart by a thickened layer of transparent adhesive or by awedge-shape insert located between them. As will be appreciated, for agiven divergence angle of the two layers, the refractive index of thematerial between the layers will determine the precise angle throughwhich light is diverted as it is transmitted therethrough.

Alternatively, a refractor, which may be a Fresnel refractor, may beattached, secured or held in a fixed relative positional relationshipwith respect to an edge region of the element. Of course, the lightdiverting means may be located not only at one edge region of theelement, for example the edge region of a windscreen adjacent the driveror passenger-side A pillar, but also at other edge regions including theupper edge region where it may assist in viewing traffic lights whenpositioned close thereto. A windscreen formed with such alight-diverting upper edge region may have this region shaded orcoloured in order to make it clear to the driver that the light arrivingthrough this region has been diverted thereby making it easier to judgeangles and distances through the uncoloured non-diverting part of thewindscreen.

The present invention also comprehends an optical element for extendingthe field of view through an edge region of an opening defined by opaqueboundaries, comprising a refractor adapted to fit against a glazingelement of the opening in the said edge region thereof and to divertlight passing therethrough towards the observer through an angle such asto bring it closer to the normal to the plane of the glazing element. Inanother aspect the present invention provides a motor vehicle windscreenhaving an optical element as defined above.

Various embodiments of the present invention will now be moreparticularly described, by way of example, with reference to theaccompanying drawings, in which:

FIG. 1 is a partial internal perspective view of the interior of a motorvehicle;

FIG. 2 is a cross-section through the line A-A of FIG. 1 useful inexplaining the principles of the present invention;

FIG. 3 is a cross section similar to that of FIG. 2, illustrating thepresence of a light-diverting optical element;

FIG. 4 is a cross-section illustrating the form of one embodiment oflight-diverting optical element;

FIG. 5 is a partial cross-section illustrating a glazing element formedas an embodiment of the present invention;

FIG. 6 is a cross-section illustrating an alternative form of opticalelement suitable for use with a glazing element;

FIG. 7 is a schematic axial section illustrating the light deflectionand useful for explaining various characteristics of the invention; and

FIG. 8 is an enlarged cross section of an optical element of Fresnelform for use with a glazing element.

Referring first to FIG. 1 a front portion of a motor vehicle passengercompartment is illustrated, showing the driver's side of a windscreenopening 12 of an LHD vehicle, defined by an A pillar 13 which forms aboundary between the windscreen 12 and a front quarter light or sidewindow 14 of a door 15. As will be appreciated, the windscreen 12 israked through an angle approaching 45 degrees, and the A pillar 13 has asignificant thickness D which, from the driver's position, canconstitute a significant barrier, particularly in view of the fact thatit, too, is strongly raked so that its effective width, parallel to theline A-A, is greater than its transverse width as represented by D. Ascan be seen in FIG. 2 an observer cannot see anything within theobscuration zone Z defined between two ray paths 16, 17 respectivelyleading from the observer's left eye L past the left edge of the pillar13 and the observer's right eye R passing the right edge of the pillar13.

Although the drawing is foreshortened for the purpose of illustration,it will be seen that an elongate object, such as a cyclist occupying avolume such as that represented by the rectangular area V lies entirelywithin the obscuration zone Z and, therefore, cannot be observed by theobserver without displacement of the eyes by moving the head from sideto side to vary the position of the obscuration zone Z. Although thismay occur if the observer is alert to the possibility of an object inthe obscuration zone, this may not happen if the observer has no reasonto suppose that the obscuration zone requires monitoring, and this couldresult in a dangerous situation, particularly if the vehicle isfollowing a curved path and/or the object in the shaded region V isfollowing a path such that the relative movement between itself and thevehicle lies along the obscuration zone Z.

If, however, according to the invention an optical element is placed atan edge region of the windscreen 12 and acts to divert the light passingthrough the windscreen 12 towards the normal to the windscreen 12, andthus towards the observer's eyes L, R then light arriving in thedirection shown by the ray 18 will reach the observer's right eye R, andthe obscuration zone Z will be reduced by the wedge-shape area betweenthe rays 17, 18 resulting, in this example, in a part of the vehicle Vbeing visible to the observer without any movement of the head beingrequired. Although the entirety of the vehicle V is not in sight, it issufficient that a part of it be visible for the observer to be alertedto its presence. If the A pillar 13 has a thickness of, for example, 100mm the observer using unaided binocular vision will require the divertedlight to be turned through no more than about 4 degrees in order toreduce the obscuration region to a minimum, that is where theobscuration region is defined between two parallel rays 16, 18 and is,therefore, no greater than the width of the barrier 13 even at adistance. In the absence of such light diversion the obscuration regionZ increases in width with increasing distance from the barrier and is,therefore, capable of obscuring larger objects at a greater distance.With this small diversion, therefore, the obscuring effect of the Apillar 13 is, consequently, effectively negated.

Of course, it is not sufficient simply to cause light diversion at thepoint A as illustrated in FIG. 2, but rather to divert light incident onthe windscreen 12 over a more extensive region adjacent the edge of thewindscreen 12 in contact with the A 0 pillar 13 (herein referred to as“an edge region”) and FIG. 3 illustrates some of the considerationarising from this. As can be seen in FIG. 3, in which the same referencenumerals have been used to identify the same or correspondingcomponents, light diversion is achieved by means of an additionalcomponent 20 fitted on the inside of the windscreen 12 in the edgeregion thereof. The precise nature of the light-diverting opticalcomponent 20 will be described in more detail below, it being sufficientat this stage to establish that it causes light transmitted therethroughto be diverted from its incident angle. If the light-diverting effectwere constant across the width of the element 20 as shown by the tworays 18 and 19 this would create its own obscuration zone in view of thefact that the first light ray 21 passing undeviated through thewindscreen 12, that is not passing through the light-diverting element20, and reaching the right eye R of the observer would effectivelycreate an obscuration region between the rays 19 and 21 therebyeffectively negating the benefit of having reduced the obscurationeffect of the A pillar 13. For this reason it is preferred that thelight-diverting properties of the optical element 20 vary across itswidth, as shown by rays 22, 23, 24 which illustrate progressively lessdeflection for rays further from the A pillar 13 until, at the very edgeof the element 20 the ray 24 passes through effectively undeviated sothat an object observed by the observer's right eye does not have astep-change as the eye passes across the boundary element 20. FIGS. 4and 5 illustrate ways in which this effect can be achieved.

Referring now to FIG. 4 a light-diverting optical element in the form ofa cylindrical negative lens is shown in section. The lens 25 asillustrated has a flat face 26, a concavely curved major surface 27, andan end face 28. In practice, of course, the substantially flat face 26may be slightly convexly curved to accommodate the curvature of awindscreen as illustrated in FIG. 3. The length of the cylindrical lens25 does not have to be as great as the length of the A pillar 13 sincethe significant region as far as potential visible objects areconcerned, occupies only a central part of the length of the A pillar13. For example the lens may be only about 200 mm long although, ofcourse, it may be the same length as the A pillar if desired. At mostthe element 25 may be about 3 mm thick (this being the width of the endface 28 and the maximum divergence angle between the face 26 and theface 27 may be in the region of six degrees. The face 27 is anacylindrical curvature with a shorter radius near the end 28 and alonger radius at the opposite or thinner end 29, which may be in theregion of 1 mm thick. An element of this form may be fitted, as shown inFIG. 5, on the rear face 30 of the windscreen 12 closely adjacent the Apillar 13, with a layer of transparent adhesive 31 securing it inposition. As will be appreciated from an observation of FIG. 5, the face26 of the element is convexly curved to match the curvature of thewindscreen 12. The element 25 may be a simple moulding, manufacturedusing an optical thermoplastic and, if not as long as the A pillar 13,may be positioned at about vision height such that the significant partof the observer's field of view lies through the element 25.

As an alternative (not illustrated) the face 27 of the element 25 may beformed in elementary segments (Fresnel form) to provide the same opticalcharacteristics as the lens illustrated in FIG. 5. In this case it ispossible, and may be preferable, to arrange that the optical axis of thelens is not parallel to the principle physical axis of the device whichis parallel to the A pillar 13. Indeed, this arrangement is alsopossible with a non-segmented lens, as illustrated in FIG. 5, but themanufacture of such a lens is more difficult. The advantage of thisconfiguration is that the image of a horizontal line in the object field(such as the horizon itself) is maintained horizontal even upondivergence by the optical element so that the horizon is not bentupwardly by the optical element as would be the case if the axis of thecylindrical surface 27 were parallel to the A pillar 13. In a Fresnellens this is achieved simply by orienting the grooves which form thesegments in such a way that they are not parallel to the principalphysical axis of the device; in this case they would be inclined at anangle such that when the device is fitted to an A pillar the grooves orribs appear substantially vertical to the observer.

Referring now to FIG. 6 this illustrates a modified laminated windscreenincorporating an edge region having lens properties as described inrelation to FIG. 4. In this drawing the windscreen 12 comprises alaminated structure having a front panel 33, a rear panel 34 and anintervening laminating adhesive 35. In the main region of the windscreen12 the front and rear panels 33, 34 are parallel to one another and theadhesive 35 is of constant thickness. In the edge region E, however, therear panel 34 is curved so as to diverge from the front panel 33. Thediverging edge region 34 e may be held spaced from the edge region 33 eof the front panel 33 by a thicker layer of laminating adhesive, or byan interposed wedge-section insert (not illustrated). As discussedabove, the angle of divergence needs to be no more than about 6 degreesat the greatest, that is at the very edge of the element, reducing tozero where the edge region E meets the main central portion M of thewindscreen. This is a particularly elegant solution from the vehiclemanufacturer's point of view as it involves no extra parts nor anychange to the vehicle assembly procedure. Furthermore, with only a smallmodification being required to the windscreen tooling and manufacturingprocess, and with possibly no extra parts being required, the cost ofincorporating the device into a windscreen is expected to be very small.In effect, this implementation consists of no more than a slightswelling of the laminating adhesive layer thickness towards the lateraledges of the windscreen. This, of course, has to be done under verycontrolled conditions in order to achieve the right curvature of therear panel 34 in the edge region 34 e.

It will be appreciated that, as least as far as its application to motorvehicle windscreens is concerned, even a small degree of light diversionat the edges of the windscreen is better than none at all in that itreduces the hazard caused by thick A pillars. In fact, the optimumsolution for windscreens may not be complete elimination of the objectfield obscuration zone because of the accommodation difficulties betweeneye and brain which may be caused when different images are presented tothe brain by the two eyes. However, experience in the use of thenow-commonly adopted aspheric driver side external rear view mirrorfitted to motor car door mirrors suggests that, although familiarisationtime may be required, this may result in a valuable improvement insafety. Partial reduction in the obscuration zone achieved according tothe invention has particular attractiveness for motor vehiclemanufacturers since a small increase in the thickness of the laminatingadhesive towards edges will provide at least a degree of light-diversionwithout it being necessary to make any modifications to the way in whichthe windscreen is fitted to the vehicle, and with no modifications tothe vehicle at all.

It is also important to note that an edge region along the substantiallyhorizontal edges of a windscreen may be provided with a light-divertingproperties either integrally as in the embodiment of FIG. 6 or by theaddition of an optical element as in the embodiment of FIGS. 4 and 5.This may provide, in the case of the upper edge of a windscreen, anextended upward view to assist in the visibility of traffic lights whichare sometime obscured by the roofline of a vehicle, especially when itis stationary close to the traffic light. An extended view through alower region of a windscreen may not be of any particular benefit unlessit can improve the view of the front part of the vehicle for manoeuvringor parking, and this would also be of benefit in the rear window ofhatchbacks, estate cars and the like.

For any embodiment of the invention used in motor vehicles it will benoted that the light diversion, as shown in FIG. 7, results in thepossibility that, with both eyes looking through the windscreen at adistant object, the one nearer the A pillar may be viewing the objectthrough the light-diverting device, whilst the other eye is viewing thesame object through an undiverted light path. Consequently a convergenceangle of the eyes is necessary in contrast to the “parallel” eyeconfiguration which would be needed if the device where not present.Convergence of the eyes is not normal when viewing distant objectsalthough, of course, does occur when viewing close objects. It is,therefore, a physical condition to which the eyes are accustomed andrequires only familiarisation to achieve comfortable observation. Byproviding an aperture with light-diverting means according to theinvention this effectively increases the size of the aperture by anamount equal to the angle that the light is deflected. This applies toboth binocular and monocular observation.

As can be seen in FIG. 8 an optical element 36 for attachment to aglazing panel may be made as a Fresnel prism. The element 36 has aplane, smooth flat front face 37 (although this may be curved as in theother embodiments) and a serrated rear face 38 comprising a plurality offacets 39 separated by risers 40. The inclination of the facets to theplane of the front face 37 varies across the width of the device fromzero at the right hand end (as viewed in the drawings) which in thiscase is the end furthest from the edge of the opening and increasing ininclination according to a quadratic relationship in which the angle αbetween a facet 39 and the plane of the front face (or the tangent tothe front face if this is curved as in the other, embodiments) increaseswith an increase in distance x from the right hand end 41 (that is theend at which α=0°) according toα=kx²where κ is a constant.

In the present embodiment, and with dimensions in the region of thoseoutlined below, κ=0.003. This is appropriate for an element in which thewidth of the element between the ends 41 and 42 is in the region of 50mm, with a minimum thickness of 2 mm at the end 41, a microstructurepitels of 0.808 mm using a material having a refractive index ofapproximately 1.53.

In this embodiment the riser draft angle is 10° at the narrow end 41 andchanges by 0.1° per mm across the width of the element. For use in amotor vehicle the dimensions and proportions discussed above ensure thatthe riser presents the minimum obstruction to the passage of light bybeing oriented approximately parallel to the light approaching theobserver's eye. At the same time the image magnitude has no step changeat the “narrow” end 41 so that there is no perceptible variation in theimage as the observer's eye sweeps across the central part of thewindscreen and on to the optical element 36 at the end 41. As itcontinues to sweep towards the edge of this windscreen (to the left asviewed in FIG. 8) the progressive change in the facet angle causes aprogressive reduction in the image width (there being no change in theimage height as the “lens” is effectively an acylindrical one) until atthe far end 42 the image width is reduced by 30% of its width whenviewed through the non-deviating central part of the windscreen.

Although illustrated as flat in this embodiment it will be understoodthat the front face 37 may be curved, for example to match the curvatureof a windscreen.

1. A glazing element for an opening defined by opaque boundaries,characterized in that it has or incorporates means for diverting lightpassing through an edge region of the element, whereby the field of viewthrough the opening is enlarged.
 2. A glazing element according to claim1, characterized in that the means for diverting light passing throughthe edge region of the element is a refractor (25).
 3. A glazing elementaccording to claim 1, characterized in that the means for divertinglight passing through an edge region of the element is integrally formedwith the said element.
 4. A glazing element according to claim 1,characterized in that the means for diverting light passing through anedge region of the element is formed separately from the said elementand fixed, attached or otherwise held in physical juxtaposition withrespect thereto.
 5. A glazing element according to claim 1,characterized in that it is adapted to fit into the said opening andhaving a central region through which light can pass substantiallyundeviated and an edge region which refracts light through an angle asit passes therethrough, the angle being greater closer to the edge ofthe element.
 6. A glazing element according to claim 5, characterized inthat it comprises at least two layers of optically transparent materialjoined face-to-face over substantially the whole area thereof, an edgeregion of each of the said two layers being formed such that the twolayers diverge from one another towards the periphery of the saidelement whereby to form a negative cylindrical lens over the said edgeregion.
 7. A glazing element (12) according to claim 1, characterized inthat the means for diverting light is so formed that there is nosubstantial surface discontinuity between the region of the element overwhich no light diversion takes place and the region of the element atwhich light is diverted.
 8. A glazing element according to claim 6,characterized in that a wedge shape insert is located between the saidtwo layers at an edge region thereof.
 9. A glazing element according toclaim 1, characterized in that a Fresnel refractor is attached, securedor held in a relative positional relationship with respect to an edgeregion thereof.
 10. A glazing element according to claim 1,characterized in that the said means for diverting light passing throughan edge region of the element is located at two opposite edge regions ofthe element.
 11. A glazing element according to claim 1, characterizedin that the said means for diverting light passing through an edgeregion of the element comprises a negative cylindrical lens.
 12. Aglazing element according to claim 1 formed as a motor vehiclewindscreen.
 13. An optical element adapted for fitting to or locating inassociation with a motor vehicle windscreen, to form a glazing elementfor an opening defined by opaque boundaries, characterized in that ithas or incorporates means for diverting light passing through an edgeregion of the element whereby the field of view through the opening isenlarged.
 14. An optical element for extending the field of view throughan edge region of an opening defined by opaque boundaries, comprising arefractor adapted to fit against a glazing element of the opening in thesaid edge region thereof and to divert light passing therethroughtowards the observer through an angle such as to bring its apparentdirection towards a central region of the glazing element.
 15. Anoptical element according to claim 14, characterized in that it is inthe form of a negative acylindrical lens.
 16. An optical elementaccording to claim 14, characterized in that it is in the form of aFresnel lens.
 17. An optical element according to claim 16,characterised in that the Fresnel lens has a plane face and a facettedface and the angle of inclination of the facets with respect to theplane face varies with the square of the distance from one edge of theelement.
 18. An optical element according to claim 17, characterized inthat the angle of inclination (α) of the facets varies according to therelation:α=kx² where: k is a constant and x is the distance from the narrow endof the element.
 19. An optical element according to claim 18,characterized in that the constant k is 0.003.
 20. An optical elementaccording to claims 16, characterized in that the pitil of the Fresnellens facets across the width of the element is in the region of 0.5 mm.21. An optical element according to claims 16, characterized in that theriser draft angle varies by 0.1° per mm across the width of the element.22. An optical element according to claim 21, characterized in that theriser draft angle is in the region of 10° at the narrow end of theelement.
 23. A motor vehicle windscreen having an optical elementaffixed or otherwise held or secured in position thereon, the opticalelement extending the field of view through the windscreen andcomprising a refractor adapted to fit against the windscreen in an edgeregion thereof and to divert light passing therethrough towards theobserver through an angle such as to bring its apparent directiontowards a central region of the windscreen.
 24. A motor vehiclewindscreen according to claim 23, characterized in that the opticalelement is a generally cylindrical negative lens oriented such that itsdirection of greatest (negative) magnification is generally horizontal.